The present invention relates generally to the art of development techniques and processing photographic plates. Specifically, the present invention is directed to a novel apparatus for ammonia development of sensitized photographic plates, such plates being used as photographic masks for use in the manufacture of microelectronic components and devices.
Heretofore, microelectronic components and devices have been made by light exposure of a photo-resist coating on a suitable substrate, such as SiO.sub.2 -- coated Si wafer, under a photographic mask, wherein desired circuit elements or pattern was recorded in an image-bearing layer. The photoresist is developed to remove portions thereof in accordance with the pattern, and the thereby exposed areas of the underlying substrate are treated to modify its characteristics. A series of patterns may be successively reproduced on the substrate, in each case applying a new photo-resist coating, exposing under an appropriate means in register with the preceding exposure, developing the photo-resist, and subjecting the exposed areas of the substrate to the desired treatment.
Conventionally, photographic masks used in the foregoing process are made with silver halide-gelatin sensitized materials -- yielding by conventional development, a mask having a silver image in a gelatin layer. The desired micro-pattern is usually produced on the mask from a large size original, made by drafting methods and reduced by optical projection to the desired size (e.g. a square of the order of 0.1 inch on a side). The micro-pattern is usually reproduced repeatedly on the mask on adjacent areas in the form of a grid (i.e. 3-4 cm. square) which is then printed in the photo-resist layer on a substrate surface. After completing development and treatment of the underlying substrate surface for each photo-resist of the series, the substrate is severed along the lines of the grid to yield a series of chips each bearing the desired components or devices for use in a microelectronic product.
Silver halide-gelatin sensitized materials have a number of serious disadvantages in the above described manufacture of microelectronic components and devices.
Exposure to light under a mask of a photo-resist layer on a substrate is ordinarily carried out by contact printing wherein the imaged gelatin layer of the mask is held in pressure contact with the coated substrate. Gelatin is not reliably durable for this purpose, and is often marred in the contacting process by scratching, abrasion, lateral movement of the contacting surfaces and by pressure contact with minute projections on the substrate surface causing socalled "star-cracking" defects and the like. To prolong the useful life of such masks, it is customary to prepare a "primary" mask with a silver image in a gelatin layer of the desired dimensions, which is used for preparation of "working" masks by contact printing on silver halide-gelatin sensitized material. The "primary" mask is not used for contact printing of the photo-resist coated substrate, but instead, the "working" masks are used for this purpose. Should these be injured, they can be readily replaced.
Moreover, silver halide-gelatin materials are inherently limited in degree of resolution, because of the granular nature of the emulsion. Loss of resolution is compounded in preparing the "working" silver halide mask from the primary mask.
In an attempt to overcome the difficulties resulting from lack of durability of the gelatin surface of "working" masks, it has been proposed to substitute masks formed by deposition of a chromium or other metal film on glass, coating with a photo-resist, exposing under a "primary" mask, developing the photo-resist, and etching away the thereby exposed areas of the chromium film. While the resulting maks are relatively durable, they suffer from defects involving lack of edge sharpness and image degradation as a result of light scattering in the photo-resist layer and of undercutting in the etching process. The highly reflecting character of the Cr surface also tends to impair resolution.
In order to overcome the various disadvantages of the gelatin silver-halide surfaced masks and the vapordeposited chromium or other metal masks, non-silver halide light sensitive material for production of photographic masks and non-silver halide masks prepared therewith, suitable for contact exposure of photo-resist-coated substrates in the production of microelectronic components and devices, was developed.
The non-silver halide type of photographic masks for the production of microelectronic components and devices are prepared by applying to a surface of a flat, rigid, dimensionally stable transparent base--especially a precision-surfaced glass plate--a thin uniform layer of a volatile, preferably organic, solvent solution of a resin adapted to form an adherent transparent film upon evaporation of the solvent, having also dissolved therein a photo-sensitizing composition comprising an azo coupling component and a light-sensitive diazonium compound susceptible to decomposition on exposure to actinic light. The composition is temporarily stabilized against coupling pending development by treatment with an alkaline developer. The photo-sensitizing composition yields a molecular dispersion of its components in the resin upon evaporation of the solvent from the layer. The quantity of solution is limited so as to provide a layer of uniform thickness-- e.g. by spraying, roller application or preferably, by applying an excess of the solution and centrifugal removal of the excess by spinning.
A clear glass plate is preferably used as the base to which the sensitizing composition is applied in preparing the non-silver halide photographic mask. These plates may range in size from about 2 .times.2 inches to about 4 .times. 5 inches and from about 0.008 to 0.15 inch thick.
After application of the light-sensitive layer to the surface of the base, and removal of the volatile solvent by evaporation, the sensitized plates are exposed to actinic light--preferably by contact exposure--under a "primary" mask bearing therein the desired pattern (e.g. as a photographic silver image) of a microelectronic component or device to be reproduced on the surface of a suitable microelectronic substrate. The plate is then developed by exposure to ammonia vapor. The latter is preferably moist but may be anyhydrous, and may, if desired, be applied at superatmospheric pressure to accelerate development. Excess ammonia can be removed by flushing with air, nitrogen or other inert gas or the like. A full and detailed description of the non-silver halide light-sensitive material, the process for making such materials, and masks prepared therewith suitable for contact exposure of photo-resist coated substrates in the production of microelectronic components and devices may be found in U.S. Pat. No. 3,744,904.
The development of the non-silver halide photo-sensitive materials and photo masks made therewith as described in the aforementioned patent, has resulted in a need for appropriate apparatus with which to expose the sensitized plates to wetted ammonia for development in making the photo masks.
Prior attempts at providing such apparatus have ranged from the use of a simple non-sealed plastic container housing a single plate, and having an opening to receive the wetted (moisturized) ammonia, to larger chambers accommodating as many as 60 plates on a rack, but also merely having a sealed door providing access for insertion and removal of the plates, and an opening for connection to a conduit to supply the moisturized ammonia to the chamber. The use of these simple containers require additional apparatus remote from the chamber for wetting pure ammonia gas to the proper level, a separate trap for removing moisture droplets from the wetted ammonia and connection means to the chamber for supplying wetted ammonia vapor to the chamber housing the plates to be developed.
Such prior developing apparatus have been found to require elaborate set-up arrangements. They have been difficult to use as they entail the assembly of a variety of separate components, containers, chambers and supply and connection conduits.
The use of multiple connections between the various containers or chambers results in the danger of inadequate seals and connections between chambers.
It is accordingly one object of the present invention to provide an apparatus for exposing the sensitized and light-exposed plates to ammonia vapors for developing the masks which avoids the disadvantages of prior apparatus.
A further object of the present invention is to provide a compact utilized structure for evenly and uniformly distributing ammonia vapors of desired moisture content to a plurality of sensitized and light-exposed plates.
A still further object of the present invention is to provide a photo plate development chamber which is capable of accommodating a plurality of plates previously sensitized with a non-silver halide light-sensitive material and exposed to actinic light in order to develop such plates to form a "working" mask for use in production of microelectronic components and devices.
Another object of the present invention is to provide an apparatus for controlling moisturization of ammonia used in the development of photo-resist masks.
A further object is to overcome the disadvantages of the prior devices used to expose the plates to ammonia by providing an apparatus containing in a single housing the various required components to provide the proper level of wetted ammonia.